Note 7 - Employee Benefit Plans (Details Textual) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2019	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Pension Plan [Member]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 3,600
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		$ 0		$ 0
Supplemental Employee Retirement Plan [Member]
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year		600		600
Other Nonoperating Income (Expense) [Member]
Net Periodic Defined Benefits Expense (Reversal of Expense), Excluding Service Cost Component		$ 1,200	$ 700	$ 2,500	$ 1,400